The present application is based on and claims priority under 35 U.S.C xc2xa7119 with respect to Japanese Patent Application No. 2000-283538 filed on Sep. 19, 2000 AD (12th year of Heisei), the entire content of which is incorporated herein by reference.
The present invention is generally directed to a hydraulic brake apparatus for a vehicle in which a brake fluid pressure is applied to a wheel cylinder for applying a braking torque to a vehicular road wheel. More particularly, the present invention is directed to a hydraulic brake apparatus for a vehicle which includes, in addition to a master cylinder, an auxiliary hydraulic pressure source and a pressure adjusting regulating device and which is capable of performing an automatic brake operation.
As a hydraulic brake apparatus which is capable of performing an automatic brake operation independent of brake pedal depression, various devices are known, as disclosed in, for example, U.S. Pat. No. 4,620,750 (corresponding to a Japanese Patent Application Publication published on Jun. 9, 1984 as Toku-Kai-Sho 59 (1984)-100045), and U.S. Pat. No. 5,114,215 (corresponding to a Japanese Patent Application Publication published on May 29, 1991 as Toku-Kai-Hei 3 (1991)-125658), each of which includes an auxiliary hydraulic pressure source and a pressure adjusting device or a pressure regulating device. These references are difficult to understand. Based only upon illustrations of these references, the device disclosed in each of the references seems to be capable of performing an automatic brake operation by utilizing a hydraulic pressure output from the pressure adjusting device.
However, in each of the aforementioned references, while the automatic brake operation is being continued under which a braking force is applied independent of brake pedal depression, if the driver depresses a brake pedal, a time duration is required for increasing the braking force, thereby hurting the brake pedal feeling. The reason is that in each reference the braking force cannot be increased for a while despite increasing the brake pedal depression since the brake fluid pressure developed during the automatic brake operation is transmitted as a reaction force to the brake pedal. In order to make the time shorter, an extremely large brake pedal depression force is required in a short period of time. In addition, a predetermined amount of time is required in order to detect such a brake pedal depression during an automatic brake operation, which makes it impossible to establish a quick transfer to another control.
Thus, in a hydraulic brake apparatus for a vehicle which includes, in addition to a master cylinder, an auxiliary hydraulic pressure source and a pressure adjusting device for performing an automatic brake operation, a need exists to increase brake fluid pressure and brake pedal feeling even if a brake pedal is depressed during automatic brake operation so that brake pedal feeling is similar to an ordinary brake pedal operation.
The present invention has been developed to satisfy the request noted above and a first aspect of the present invention provides a hydraulic brake apparatus for a vehicle which comprises:
A master cylinder advances a master piston, depending on an operation of a brake operation member, to increase a pressure of a brake fluid supplied from a brake fluid reservoir. The master cylinder outputs the resultant brake fluid as a brake fluid pressure.
A power piston is placed at a rearward portion of the master piston to define a power chamber. The power piston is advanced by a hydraulic pressure in the power chamber to advance the master piston.
An auxiliary hydraulic pressure source outputs a power hydraulic pressure by increasing the pressure of the brake fluid supplied from the reservoir.
A pressure adjusting device is connected to the auxiliary hydraulic pressure source, is connected to the reservoir to adjust the power hydraulic pressure to a value which is output from the auxiliary hydraulic pressure source, and supplies the adjusted power hydraulic pressure to the power chamber.
The pressure adjusting device includes a valve device and a driving device.
The valve device is provided in the power piston and establishes, depending on at least the operation of the brake operation member, a changeover between a first position at which the power chamber is pressurized to atmospheric pressure and a second position at which the power chamber is brought into fluid communication with the auxiliary hydraulic pressure source.
The driving device hydraulically drives the valve device, independent of the operation of the brake operation member.
The driving device, when applied with hydraulic pressure, switches the valve device to the second position, and urges the power piston to advance, without transmitting the resultant force to the brake operation member. The power piston is advanced against a reaction force to the power piston which results from the hydraulic pressure output from the master cylinder. The driving device, when applied with no hydraulic pressure, retains the valve device at the first position.
A second aspect of the present invention is to provide a hydraulic brake apparatus in which the valve device includes a spool which is movable in the axial direction in the power piston. The power chamber is constructed to be in fluid communication with the auxiliary pressure source and the reservoir when the spool is in advancing and retracting positions, respectively, relative to the power piston. The spool is advanced when the driving device is applied with hydraulic pressure.
A third aspect of the present invention is to provide a hydraulic brake apparatus in which the driving device is in the form of a stepped portion formed at an outer surface of the spool. The stepped portion is constructed such that a rearward side of the stepped portion is capable of receiving a hydraulic pressure in the power piston.
A fourth aspect of the present invention is to provide a hydraulic brake apparatus in which the hydraulic pressure to be applied to the driving device is a hydraulic pressure output from the auxiliary hydraulic pressure source.
A fifth aspect of the present invention is to provide a hydraulic brake apparatus in which an electromagnetic valve device is controlled. The electromagnetic valve device is disposed between the auxiliary hydraulic pressure source and the driving device and regulates the hydraulic pressure to a desired pressure value, which is to be applied to the driving device from the auxiliary hydraulic source.
A sixth aspect of the present invention is to provide a hydraulic brake apparatus in which the master piston and the power piston are accommodated in a cylinder. The cylinder is provided therein with a passage which establishes fluid communication between the power chamber and a pressure chamber defined between the master piston and the power piston. The passage is provided therein with a normally open differential-pressure responsive valve which is closed depending on a pressure increase in the second pressure chamber.
A seventh aspect of the present invention is to provide a hydraulic brake apparatus further including an input member and a reaction rubber disc. The input member is moved in the power piston at a rearward side of the spool for transmitting the operation of the brake operation member to the spool. The reaction rubber disc is disposed in the power piston at a frontward side of the spool for transmitting a reaction force from the master piston to the spool when the brake operation member is operated.
An eighth aspect of the present invention is to provide a hydraulic brake apparatus further including a plunger which is placed between the spool and the reaction rubber disc in a slidable fashion. The plunger is accommodated in a space which is in fluid communication with the reservoir.